.TH std::basic_filebuf::pbackfail 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::basic_filebuf::pbackfail \- std::basic_filebuf::pbackfail

.SH Synopsis
   protected:
   virtual int_type pbackfail( int_type c = Traits::eof() )

   This protected virtual function is called by the public functions
   basic_streambuf::sungetc and basic_streambuf::sputbackc (which, in turn, are called
   by basic_istream::unget and basic_istream::putback).

   1) The caller is requesting that the get area is backed up by one character
   (pbackfail() is called with no arguments), in which case, this function re-reads the
   file starting one byte earlier and decrements basic_streambuf::gptr(), e.g. by
   calling gbump(-1).
   2) The caller attempts to putback a different character from the one retrieved
   earlier (pbackfail() is called with the character that needs to be put back), in
   which case
   a) First, checks if there is a putback position, and if there isn't, backs up the
   get area by re-reading the file starting one byte earlier.
   a) Then checks what character is in the putback position. If the character held
   there is already equal to c, as determined by Traits::eq(to_char_type(c),
   gptr()[-1]), then simply decrements basic_streambuf::gptr().
   b) Otherwise, if the buffer is allowed to modify its own get area, decrements
   basic_streambuf::gptr() and writes c to the location pointed to gptr() after
   adjustment.

   This function never modifies the file, only the get area of the in-memory buffer.

   If the file is not open (is_open()==false, this function returns Traits::eof()
   immediately.

.SH Parameters

   c - the character to put back, or Traits::eof() to indicate that backing up of the
       get area is requested

.SH Return value

   c on success except if c was Traits::eof(), in which case Traits::not_eof(c) is
   returned.

   Traits::eof() on failure.

.SH Example

    This section is incomplete
    Reason: no example

.SH See also

             puts a character back into the input sequence, possibly modifying the
   pbackfail input sequence
   \fB[virtual]\fP \fI(virtual protected member function of std::basic_streambuf<CharT,Traits>)\fP

   sungetc   moves the next pointer in the input sequence back by one
             \fI(public member function of std::basic_streambuf<CharT,Traits>)\fP
   sputbackc puts one character back in the input sequence
             \fI(public member function of std::basic_streambuf<CharT,Traits>)\fP
   unget     unextracts a character
             \fI(public member function of std::basic_istream<CharT,Traits>)\fP
   putback   puts a character into input stream
             \fI(public member function of std::basic_istream<CharT,Traits>)\fP

.SH Category:
     * Todo no example
